Suddenly I cannot find my valuable notes in the sidebar.

Hi Jim, unfortunately, it seems that this extension is still around but isn't being maintained/supported in the past few years. * https://addons.mozilla.org/firefox/addon/notes-by-firefox/ * https://github.com/mozilla/notes Did your Firefox switch from the classic sidebar design to the more modern one with the vertical button bar at the left? If you think Notes requires the classic sidebar, try this to switch back: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button accepting the risk. ''More info on about:config:'' [[Configuration Editor for Firefox]]. ''The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.'' (2) In the search box in the page, type or paste '''sidebar.revamp''' and pause while the list is filtered (3) Double-click the preference to switch the value from true to false Does that help? I don't know how many more versions the classic sidebar will be around, so please export/archive/save your Notes data outside of the extension in preparation for that eventuality.